Lithium-titanium-zinc ferrites

ABSTRACT

Microwave ferrites with narrow resonance linewidths, good temperature performance, low losses, low costs, and rectangular hysteresis loops are made from a lithium-titanium ferrite containing a small amount of zinc. In addition, small amounts of copper or manganese can be present in the ferrites.

O Umted States Patent [151 3,644,207 Baba et a1. Feb. 22, 1972 [54]LlTHIUM-TlTANIUM-ZINC FERRITES 3,177,145 4/1965 Brownlow ..252/62.61 X72] lnvcmors: Paul D. Balm San Carlos; Gman Michael 3,483,126 12/1969Sara et a1. ..252/62.6 X

Argentina, Belmont, both of Calif.

- Primary Examiner-Tobias E. Levow od t al f. [73] A'sslgnee AmpexCorporation, Redwo C1 y C Assistant Examiner]. Cooper [22] Filed: Oct.2, 1969 A"omeiy Rbel-t Clay [21] App1.No.: 863,372

[57] ABSTRACT [52] U.S.Cl ..252/62.59, 252/626, 25266226612, Microwaveferrites with narrow resonance newidths, good Int Cl gg temperatureperformance, 10w losses, low costs, and rectangula! hysteresis loops aremade from a lithiummanium ferrite [58] Fleld of Search ..252/62.59,62.6, 62.61 62.62 containing a Small amount of zinc. In addition, smallamounts [56] References Cited of copper or manganese can be present inthe ferrites.

UNITED STATES PATENTS 1 Claims, No Drawings 3,065,182 11/1962 Aghajanian..252/62.6l X 7 LlTI-IIUM-TITANIUM-ZINC FERRITES The invention describedherein was made in the course-of a contract with the United StatesDepartment of Air Force.

SUMMARY OF THE INVENTION At the present time, garnets are ordinarilyemployed at microwave frequencies. However, garnets are expensive andhave poor temperature performance. Although it has been suggested thatferrites might be used, the losses have been.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following preparativeprocedure is used in compounding ferrite materials in accordance withthe present invention:

Oxides of the constituent metal ions are generally employed whenpossible. In instances where the chemical instability of the oxide of aparticular metal ion causes said oxide to be an impure and unreliablecompound, the. anhydrous carbonate of the metal ion is used. The rawmaterials are weighted out in stoichiometric proportions and are wetmixed for 1 hour or more in a ball mill. The resulting slurry is thendried at around -l C. and the dried raw material mixture is then forcedthrough a standard -mesh screen for ease of handling.

The screened oxide mixture is then loaded into refractory boats. Theboats are placed in a box-type furnace, and heated to a predeterminedtemperature. The exact temperature can vary from 700 to 900 C. Theobject of this step is twofold: the primary object is to providesufficient energy to react the oxide mixture to a 70 percent ferrite 30percent oxide mixture by a solid state reaction. The secondary objectiveis the simple thermal'decomposition of any carbonates used.

The reacted mixture is generally characterized by a relatively largepredominant particle size. Before the mixture can be shaped and sinteredinto a single phase ferrite body the particle size must be reduced. Ballmilling is employed in essentially the same manner as outlined above.The ferrite-oxide slurry is then dried at around 80 C. to a fine powder.

The powder is then mixed with a binder as is well known to those skilledin the art. Wide latitude is permissible in the selection of binders. Atypical binder is polyvinyl alcohol.

The addition of the binder can be carried out in the second ball millingstep, or in an additional step employing any sort of method facilitatinguniform distribution of the substance used as a binder. The binderimpregnated powder is then shaped in tool steel dies with enoughpressure to facilitate uniform compaction.

The pressed shapes are then sintered at temperatures ranging from 950 tol, 1 50 C. in atmospheres of oxygen or air.

The novel ferrites of the present invention have the followingcomposition.

where 0.05 s w s 0.3

and 0.30 s x s 0.95

0 s s 0.2 0 szs0.2

The following nonlimiting examples illustrate various preferredembodiments of the invention. In the examples, Ex

amples l and 3 illustrate com ositiqns which contain zinc whr e Examples2 and 4 show su stantially the same composition without the addition ofzinc, showing the beneficial effect of the zinc addition.

EXAMPLE 1 A ferrite having the composition where x=0.7, y=0, z=0 andw=0.l was prepared by the above procedure. The reaction step wasperformed at 900 C. The sintering step was performed at 1,100 C. in anoxygen atmosphere. The ferrite had a coercive force of 2.26 oersteds, aremanence of 709 gauss, a saturation magnetization of 825 gauss, amagnetic loss of 0 decibels per inch, a dielectric loss of 0.7 decibelsper inch, a resonance linewidth of 360 oersteds, and a density of 3.64grams per cubic centimeter.

EXAMPLE 2 Example I contains zinc while Example 2 does not contain zinc.The material of Example 1 is superior because it exhibits a lowercoercive force, a higher remanence, a lower magnetic loss, a narrowerresonance linewidth, and a higher density than does 2. I

EXAMPLE 3 A ferrite was made where x=0.55, y=0. l, z=0.l and w=0. 1. Ithas a coercive force of 4.02 oersteds, a remanence of 670 gauss, asaturation magnetization of 915 gauss, a dielectric loss of 0.52decibels per inch, a resonance linewidth of 375 oersteds, and a densityof 4.02 grams per cubic centimeter.

EXAMPLE 4 A ferrite was made where x=0.55, y=0.l, z=0.l and w=0. It hada coercive force of 5.15 oersteds, a remanence of 535 gauss, asaturation magnetization of 661 gauss, a dielectric loss of 0.58decibels per inch, a resonance linewidth of 550 oersteds, and a densityof 3.09 grams per cubic centimeter.

Example 3 contains zinc while Example 4 does not contain zinc. Thematerial of Example 1 is superior because it exhibits a lower coerciveforce, a higher remanence, a lower dielectric loss, a narrowerlinewidth, and higher density than does 4.

We claim:

1. A lithium-titanium-zinc ferrite having the formula:

